Making Improvements to Today s Natural Gas Analysis Systems

Transcription

1 Making Improvements to Today s Natural Gas Analysis Systems Hiroyuki Aikawa, Ryosuke Kamae, Yuki Hashi, PhD, Shimadzu (China) Co., Ltd. 1. Introduction In recent years, driven mainly by rising energy demand, many regions of the world have witnessed a resurgence in the production of petrochemicals. New technologies for mining the deep shale deposits for natural gas have been refined in the U.S. and made extraction of these deposits economically viable. In China, new technologies for turning coal into olefins by way of methanol (CTO: Methanol to Olefin) has fueled its economy and provided feedstocks for the chemical and polymer industries. In every petrochemical process, measurement and quality control are essential. Processing plants must characterize the incoming raw materials. Finished products must be evaluated to ensure specifications are met. Every time natural gas changes hands, an analysis is done to determine its energy content and thus its value. There is a need for scientific instrument manufacturers to match the innovation shown by the petrochemical industry by producing high-precision, accurate equipment that this industry can rely on. Shimadzu Corporation is ready to meet this challenge with a lineup of NGA systems (Natural gas analyzers). Our NGA system can include permanent gases such as H 2, N 2 and light hydrocarbons from C 1 to C 6 +. Samples may take the form of a gas or high-pressure liquid state. Our systems can combine standard analyses with extended analysis of condensates. We have the tools to build the systems that meet the demand of today s petrochemical industry. In this article, improved technologies in these NGA systems will be introduced Shimadzu NGA system Table 1 shows two typical Shimadzu NGA systems. While GC-214NGA1 is a packed columns-based system and all components are detected by two TCDs, GC-214FNGA1 is a PLOT columns-based system (except for He, H 2 detection) and all components are detected by two TCDs and one. GC-214FNGA1 is called a Fast NGA system since the analysis time is only 1 minutes, enabling high productivity. The detection range of components with this system is shown in Table 2. This system consists of four sample loops and eight columns. O 2, N 2, CH 4 and CO are separated by an Rt-MS-5A plot column (.53 mmi.d., 5 µm, 3 m) and CO 2, C 2 H 6 and H 2 S are separated by an Rt-Q plot column (.53 mmi.d., 2 µm, 3 m). These components are detected by TCD1. In order to avoid an overlapping of eluted peaks from two columns, the Rt-Q plot column analysis is started after the Rt-MS-5A plot column analysis has finished. This is referred to as a Delay injection technique. C 3 or higher hydrocarbons are separated by the Rtx-1 + column (.32 mmi.d., 3. µm. 3 m) and detected by. C 6 components are back-flushed as a single peak. H 2 and He are separated by an MS-13X packed column (6/8 mesh, 2.1 mmi.d., 1. m) and detected by TCD2. (Fig. 2, 3) One of the outstanding characteristics of this system is its short analysis time. This results from adapting a.32 mmi.d. capillary column for C 3 or higher hydrocarbons separation. Furthermore, a split line is placed in front of the capillary column in order to maintain good peak shape. 2. Typical Natural Gas Analyzers (NGA) 2 1. Requirements of typical NGA Systems Natural gas processing occurs in a number of steps. It begins with the extraction of the raw gas at the well head. Analyses occur at this stage to determine the water content, hydrogen sulfide and aromatic hydrocarbon content. These parameters are important in determining the best processing options and are closely monitored by the EPA if there is a flare associated with the well. From the source, the gas is transported to the processing plant by truck, train or pipeline, where again it is analyzed to determine its chemical composition. Finally, as the processing plant sells the finished, dry, sulfur-free natural gas to the distributor or end user, another analysis is done to determine the price based on the energy content of that particular lot. This is done by taking the percent composition of that lot of gas and calculating its BTU content. For each of these steps, Shimadzu offers a variety of NGA systems to comply with industry-standard methods such as those developed by ASTM, GPA, ISO and UOP. In many cases, multiple methods can be combined in a single GC to save on bench space and optimize a lab s budget. Fig. 1 NGA System based on GC

2 Table 1 NGA system configuration, target compounds and analysis time Table 2 Detection range of components of the Fast NGA system Model Name GC-214NGA1 GC-214FNGA1 Standard Method Flow Controller ASTM-D1945 ASTM-D3588 GPA-2261 Dual AFC AUX-APC ASTM-D1945 ASTM-D3588 GPA-2261 Dual AFC AUX-APC Valve Numbers 3 4 Column Numbers 6 8 Type of Detector Dual TCD Dual TCD, Target Compounds He, H2, O2, N2, CH4, CO, CO2, C2-C5, H2S, C6 + He, H2, O2, N2, CH4, CO, CO2, C2-C5, H2S, C6 + Analysis Time 17 min 1 min No Concentration Range Name of Compound Detector Low Conc. High Conc. He.1% TCD-2 H2.1% TCD-2 O2.1% 2.% N2.1% 5.% CO.1% 5.% CO2.1% 2.% C2H6.1% H2S.1% 3.% CH4 2.% 1.% C3H8.1% i-c4h1.1% n-c4h1.1% i-c5h12.1% 2.% n-c5h12.1% 2.% C6 +.1%.5% O2, N2, CH4 and CO (CO, CH4) CO2, C2 and N2S H2 C6+ and C1, C2 C5 He and H2 Fig. 2 Flow diagram of the Fast NGA system 18

3 2. uv(x1,,) C 3H Rtx i-c 4H C 6 + n-c 4H 1 n-c 5H 12 i-c 5H min Channel of uv(x1,) Rt-Q N 2 CH 4 Rt-MS-5A CO CO 2 C 2H 6 H 2S O min Channel of TCD1 uv(x1,) 4. MS-13X packed H He min Channel of TCD2 Fig. 3 Chromatogram of the Fast NGA system 19

4 3. NGA System using the Barrier Discharge Ionization Detector () 3 1. The barrier discharge ionization detector () The is a highly sensitive detector that creates ionization from dielectric barrier discharge plasma. It offers highly sensitive detection of all compounds except helium and neon. Plasma is generated by applying a high voltage to a quartz dielectric chamber in the presence of helium. Compounds that elute from the GC column are ionized by this He plasma, then captured with collection electrodes and described as peaks (Fig. 4). The has the advantage of providing high-sensitivity detection of both inorganic and organic compounds at the sub ppm level. This advantage may potentially simplify gas analysis systems like the NGA system Ultrafast NGA system with The ultrafast NGA system s configuration consists of three sample loops, six columns and two detectors: and. The detection range of components is shown in Table 3. H 2, O 2, N 2 and CO are separated by an Rt-MS-5A plot column (.53 mmi.d., 5 µm, 3 m) whereas CO 2, C 2 H 4, C 2 H 6, C 2 H 2, H 2 S are separated by an Rt-Q plot column (.53 mmi.d., 2 µm, 3 m). The ends of the two columns are joined together and the components are detected by the (Figs. 5, 6). CH 4 and C 3 or higher hydrocarbons are separated by an Rtx-1 column (.53 mmi.d., 5. µm. 6 m) and detected by. Table 3 Detection range of components of the Ultra-Fast NGA system Column Fig. 4 Quartz tube (dielectric substance) He plasma Barrier discharge ionization detector () He No. Name of Compound Concentration Range Low Conc. High Conc. Detector 1 H2.1% 2 O2.1% 2.% 3 N2.1% 5.% 4 CO.1% 5.% 5 CO2.1% 2.% 6 C2H4.1% 7 C2H6.1% 8 C2H2.1% 9 H2S.1% 3.% 1 CH4 2.% 1.% 11 C3H8.1% 12 i-c4h1.1% 13 n-c4h1.1% 14 i-c5h12.1% 2.% 15 n-c5h12.1% 2.% 16 C6 +.1%.5% (CO, CH 4) CO 2, C 2 and H 2S H 2, O 2, N 2, CH 4 and CO Fig. 5 Part of flow diagram of the Ultrafast NGA system (Channel of ) 2

5 uv(x1,) 1. N2 9. H2 O C2H4 C2H6 CO2 4. CO C2H2 H2S min Fig. 6 Chromatogram using the Ultrafast NGA system (Channel of ) uv(x1,) 7. C6 + CH4 6. C2H C3H8 i-c4h1 n-c4h1 i-c5h12 n-c5h min Fig. 7 Ultrafast NGA system Chromatogram (Channel of ) Table 4 Repeatability of peak areas of the Ultrafast NGA system (Channel of ) ID Compound Name Mean Area RSD% 1 H2 (16.2%) 1,221,8 1,217,638 1,22,585 1,221,434 1,219,877 1,221,352 1,22, O2 (4.82%) 1,21,943 1,21,78 1,23,779 1,21,378 1,199,38 1,23,229 1,21, N2 (9.98%) 1,514,715 1,511,981 1,517,955 1,514,142 1,514,211 1,518,9 1,515, CO (1.2%) 486, , , ,13 487, , , CO2 (1.96%) 1,334,791 1,337,94 1,338,552 1,336,785 1,331,65 1,326,637 1,334, C2H4 (.998%) 1,51,314 1,513,12 1,514,393 1,512,294 1,54,769 1,499,412 1,59, C2H6 (1.%) 2,19,195 2,114,54 2,115,465 2,112,86 2,12,367 2,95,589 2,18, C2H2 (.51%) 576,87 576,85 576,73 576, , , , H2S (.525%) 512,847 58,727 51, ,634 58, ,887 51, A key aspect of this system is the use of one instead of two TCDs for detecting inorganic components. This stems from the ability of the to provide high-sensitivity detection of all components. In addition, reducing the number of detectors simultaneously reduces the number of columns required. In other words, the simplifies analysis. In addition, because the is very sensitive and shows a saturated response to highly-concentrated components, unlike TCD, a small volume of sample loops (2 or 5 µl) is used in the stream, and introduced samples are split at the front of columns. Finally, the main component CH 4 is detected by another stream in an. In parallel with CH 4 detection by, shortening the analysis time of the stream resulted in an analysis time of less than 5 minutes. As Table 4 shows, the Ultrafast NGA system provides good repeatability of peak areas with the channel. The Ultrafast NGA system combines the best properties of high productivity and reliability, allowing operators to optimize their workflow. 4. Conclusion Shimadzu has offered various sorts of NGA systems for decades. Current systems, such as the Fast NGA system and Ultrafast NGA system, enable high productivity and reliability. These systems features are based on innovative ideas, such as taking advantage of capillary columns and adapting new detector technology. We will continue to develop and refine systems to meet the demands of the energy sector. 21